In a continuous casting machine for continuously casting steel, molten steel is poured from a tundish into a rectangular tube-shaped mold and the molten steel is cooled through contact with the mold, a cast piece, in which unsolidified steel is present at the center portion thereof, is continuously drawn downward, and molten steel is continuously poured into the mold. The cast piece drawn downward out of the mold is water cooled by water spray. Finally, after completely solidified, the cast piece is cut into pieces of predetermined length and sent to a downstream process, that is, rolling.
In the mold, molten steel is brought into contact with the inner side surface of the mold, so that the molten steel is cooled and a solidified shell is formed. In order to prevent the solidified shell from adhering to the inner side surface of the mold, the mold is oscillated in the vertical direction (Patent Document 1). This prevents the cast piece from adhering to the inner side surface of the mold, so that it is possible to smoothly draw the cast piece out of the bottom of the mold.
FIG. 11 is a schematic diagram showing an eccentric cam-type mold oscillator. As shown in FIG. 11, an arm support portion 3 is mounted on a partition wall 6. One end portion of a sub-arm 4 and a midpoint portion of a main arm 5 are respectively supported in a swingable manner by horizontal pivot shafts 3a and 3b provided in the arm support portion 3. A mold 1 is supported on an oscillation table 2 and oscillated together with the oscillation table 2. The other end portion of the sub-arm 4 and one end portion of the main arm 5 are respectively connected to horizontal pivot shafts 2a and 2b of the oscillation table 2 in a swingable manner. In this way, the main arm 5 and the sub-arm 4 constitute a parallel link, so that the four points, the pivot shafts 3a, 3b, 2b and 2a, operate in relation to one another with distances therebetween being fixed. The distance between the pivot shafts 2a and 2b, the distance between the pivot shafts 3a and 3b, the distance between the pivot shafts 3a and 2a, and the distance between the pivot shafts 3b and 2b are set so that extensions of line segments 2c and 2d cross each other at a swing arm center 1a, the line segment 2c connecting between the pivot shaft 3a and the pivot shaft 2a, the line segment 2d connecting between the pivot shaft 3b and the pivot shaft 2b. Accordingly, when the parallel link (the main arm 5 and the sub-arm 4) swings, the mold 1 is oscillated (swings) in the vertical direction about the swing arm center 1a along an arc with a certain curvature radius.
A motor 10 is mounted on an installation floor with the pivot shaft being horizontally positioned. The rotary shaft of the motor 10 is provided with an eccentric cam 9. The eccentric cam 9 and a pivot shaft 7 at the other end of the main arm 5 are connected via a link 8. Accordingly, rotation of the motor 10 causes rotation of the eccentric cam 9, which in turn causes vertical movement of the link 8 via the eccentric cam 9. The vertical movement of the link 8 causes the main arm 5 to swing, which in turn causes the sub-arm 4 to swing. In this way, the mold 1 is oscillated in the vertical direction.
FIG. 12 is a schematic diagram showing a hydraulic servo-type mold oscillator. In this hydraulic servo-type mold oscillator, a hydraulic servo cylinder 11 is installed in place of the eccentric cam. In the hydraulic servo cylinder 11, an upper end of a piston 12 is rotatably connected to a pivot shaft 7, so that the other end pardon (pivot shaft 7) of a main arm 5 is caused to reciprocate in the vertical direction by the piston 12 driven by the hydraulic servo cylinder 11.
FIG. 13 is a schematic diagram showing an electrically driven servo-type mold oscillator. In this electrically driven servo-type mold oscillator, an electrically driven servo actuator 20 is installed in place of the eccentric cam shown in FIG. 11. FIG. 14 is a schematic diagram showing the electrically driven servo actuator 20. A base 21 is mounted on an installation floor. A servo motor 22 and a cylinder tube 33 are installed on the base 21. The servo motor 22 is installed so that a rotary shaft 23 is positioned in the base 21 with the axial direction of the rotary shaft 23 being directed downward in the vertical direction. Tile rotary shaft 23 is provided with a pulley 24. A threaded shaft 29 of a ball screw is rotatably installed via angular bearings 55 with the axial direction of the threaded shaft 29 being directed in the vertical direction, and a lower part of the threaded shaft 29 is positioned in the base 21. A pulley 25 is fixed to a lower end portion of the threaded shaft 29. A belt 26 is looped between the pulley 24 and the pulley 25. Accordingly, forward and reverse rotation of the motor 22 causes forward and reverse rotation of the threaded shaft 29 via the belt 26.
In the cylinder tube 33, a nut-side shaft 31 is fixed to a ball nut 30 coaxially with the threaded shaft 29 that is positioned with the central axis thereof being directed in the vertical direction. The ball nut 30 is screw-fitted on the threaded shaft 29 with balls interposed therebetween. Forward and reverse rotation of the threaded shaft 29 causes the ball nut 30 to move in the vertical direction. The nut-side shaft 31 is fixed to the upper end of the ball nut 30 with the axial direction of the nut-side shaft 31 being directed in the vertical direction. The nut-side shaft 31 is supported by ball splines 34 so as to be able to move in the vertical direction. The upper end of the nut-side shaft 31 protrudes upward from an upper portion of the cylinder tube 33. The upper end of the nut-side shaft 31 is connected to the pivot shaft 7 at the other end of the main arm 5.
In the electrically driven servo-type mold oscillator, the belt 26 transmits rotational driving force produced by forward and reverse rotation of the rotary shaft 23 of the servo motor 22 to the threaded shaft 29 in the cylinder tube 33, which causes forward and reverse rotation of the threaded shaft 29. The forward and reverse rotation of the threaded shaft 29 causes the ball nut 30 screw-fitted on the threaded shaft 29 to move in the vertical direction, which in turn causes the nut-side shaft 31 fixed to the upper end of the ball nut 30 to move in the vertical direction. In this way, a main arm 5, to which an upper end portion of the nut-side shaft 31 is connected via a pivot shaft 7, swings about a pivot shaft 3b. The swinging motion of the main arm 5 is followed by swinging motion of a sub-arm 4, which in turn causes a mold 1 to oscillate in the vertical direction.